Clarify some important factors for a population maintenance of endangered species is necessary for establishing conservation measures. Drosera anglica is one vulnerable species in circum-boreal peatland. Habitat loss and drainage from agriculture have been assumed to be the main factors for decline of D. anglica. Despite preserve of the habitat, the population of D. anglica reached a critical size in many habitat across the world, and in some locations, the species is predicted to be extinct within the next decade. Elucidate the factors that is required to conserve the population of D. anglica may not only contribute for this species survival, but also for understanding the maintenance mechanism of diversity in peatland. Generally, it has been said that D. anglica is less tolerant of desiccation than D. rotundifolia, which occurs in a wider range of habitat, and prefers full sun. But there was no difference on seedling survival and growth between two species with reference to water level in my master thesis research. Therefore, I tested the hypothesis that the habitat of D. anglica was more restricted by light condition than D. rotundifolia.
In July 2011, eight 300 ×50 cm plots were randomly set in co-occured area of the two Drosera species in Sarobetsu and Oze mire. Using an intrinsic conditional autoregressive (CAR) model, I analyzed microscale distribution patterns of D. anglica comparing with D. rotundifolia in response to ground height and vegetation cover. The occurrence probability of D. anglica was negatively correlated with vegetation cover, but not with ground height. In seeding experiment, the shading treatment decreased seedling growth of D. anglica, whereas didn’t affect the growth and survival of D. rotundifolia. These results suggested that D. anglica preferred light microhabitats without another species shading for full seedling growth. Maintaining microhabitats where other plants hardly establish, e.g., areas of perennial water saturation, may be considered as a key factor in the conservation of D. anglica.